1. Field of the Invention
The present invention relates to a recording apparatus for recording video information or audio information by variable length coding and to a reproducing apparatus for reproducing the recorded information.
2. Description of the Prior Art
To replace the analog video tape recorder (VTR) for recording a video signal on a magnetic tape directly as an analog signal, recently, it is being promoted to develop and commercialize a digital VTR which converts the video signal from analog signal into digital signal, and processes and records the digital signal, with the purpose of improving the picture quality and preventing deterioration at the time of dubbing, for example.
Its operation is explained below by reference to the block diagram of a signal processing unit in FIG. 31.
The video signal which is converted from analog to digital (A/D) by the known art is fed into a discrete cosine transform (DCT) circuit 401 in order to undergo DCT for the purpose of data compression. In the DCT circuit 401, DCT is conducted in a unit of 8 pixels.times.8 pixels (hereinafter called a DCT block), and the transformed signal is produced in the unit of 1 pixel into a quantizing circuit 402 (the data of 64 transformed pixels is produced by 1 DCT). In the quantizing circuit 402, the input data is quantized by every 1 pixel, and is put into a variable length coding circuit 403 for coding at high efficiency. In the variable length coding circuit 403, according to a known algorithm such as two-dimensional Huffman code (to determine the code word from the number of zero runs and the succeeding non-zero values, and the greater the number of zeros in the input data, the smaller becomes the number of code words in the DCT block), the data is converted into variable length code according to the zero run length and amplitude value of the quantized data, and the output is sent into an error correction coding circuit 404. The length of the output data row of the variable length coding circuit 403 varies with the quantized value and is not in a constant length. In the error correction coding circuit 404, an error correction code such as Reed Solomon code is added so that the error occurring at the time of reproduction may be corrected, and its data row is produced to a modulation circuit 405. The output data row is modulated in the modulation circuit 405, and is recorded and amplified in a recording circuit 405, and is recorded on a tape 500 through a magnetic head 407.
In reproduction, the signal reproduced from the tape 500 by the magnetic head 407 is sufficiently amplified in a reproduction amplifying circuit 408, and demodulated in a demodulation circuit 409, and is put into an error correction circuit 410. In the error correction circuit 410, the error occurring due to dropout or the like on the tape is checked, and the corrected data is put into a variable length decoding circuit 411. The variable length decoding circuit 411 decodes the zero run length and amplitude value from the signal coming out of the error correction circuit 410. An inverse quantizing circuit 412 inversely quantizes the amplitude value including the obtained zeros and con obtain the signal generated right after DCT. This signal is converted into a signal on the time axis by an inverse DCT circuit 413, and an analog video signal is produced through a digital/analog conversion circuit (not shown), and is interfaced with a monitor or device apparatus.
In this conventional constitution, however, since the signal is put into the error correction coding circuit 403 right after variable length coding, the data is recorded in the tape continuously from the low frequency components to high frequency components in one DCT block. That is, assuming the data array in the DCT block unit, it is regarded as follows:
(DCT1: low range to high range) to (DCT2: low range to high range) to (DCT3: low range to high range), and so forth.
Therefore, in reproduction, when a data string that cannot be corrected in the error correction circuit 410 because of a large error scale occurs, since variable length coded signals are recorded, it is impossible to distinguish the divisions of data, and the data after the error onset cannot be used at all, that is, normal reproduction after the error is disabled, and moreover it is practically impossible to realize special reproduction such as high speed reproduction that does not trace the recording tracks normally, involving a high risk of occurrence of such error.
To realize such format, however, the data once coded in variable length must be reshuffled, which requires complicated circuitry and a very large memory. In particular, it can not be applied an apparatus requiring real time processing at high speed, such as moving picture processing.
It is hence a primary object of the invention to solve the problems of the conventional recording apparatus and reproducing apparatus.